Closed-cell polyurethane foams are widely used for insulation purposes in building construction and in the manufacture of energy efficient electrical appliances. To prepare these foams, expansion or blowing agents are required. Historically, trichlorofluoromethane (CFC-11) has been the choice blowing agent for these foams as well as for the polyurethane/polyisocyanurate foams. CFC-11, along with 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113), has been the blowing agent of choice in the preparation of phenolic foams.
However, in Sept. 1987, when the United Nations, through its Environmental Program Unit, issued a proposal calling for the reduction in world-wide production of fully halogenated chlorofluorocarbons such as CFC-11 and CFC-113 (ratified on Jan. 1, 1989), there began a search for an acceptable substitute for CFC-11. That is, there was an urgent need for an effective blowing composition that would contribute little or, preferably, nothing to the stratospheric ozone depletion process nor to the global warming process known as the "greenhouse effect".
HCFC-123, which is a hydrogen-containing and, therefore, a "not fully" halogenated chlorofluorocarbon, has now become the choice substitute for CFC-11 in blowing compositions. However, the blowing agent market demands that the HCFC-123 contain less than 1% of any isomeric impurities such as HCFC-123a and HCFC-123b. It had been found that these impurities, particularly HCFC-123a, have objectionable reactivity toward the other components in the blowing formulations.
Removing the objectionable isomeric dichlorotrifluoroethanes is extremely difficult. The isomers are too close boiling for economic separation by conventional methods.